Low swage load fastening system and method

ABSTRACT

A collet for a fastener installation tool having a pull section with a fastener engagement end and a plurality of teeth. The teeth include a first tooth with a first inner diameter, and each of the remainder of teeth includes a second inner diameter, the first inner diameter being greater than the second inner diameter. The pull section includes a protrusion extending from the fastener engagement end, thereby extending the length of the pull section. The pull section includes a cross-sectional thickness, wherein the collet is adapted to engage a pin member having a locking portion with a first diameter and a pull portion with a smaller second diameter. An increase in the difference between the first diameter of the locking portion and the second diameter of the pull portion of the pin member allows for a corresponding increase in the cross-sectional thickness of the collet, thereby extending the fatigue life of the tool.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of prior U.S.application Ser. No. 12/823,339, filed on Jun. 25, 2010, which is acontinuation application of prior U.S. application Ser. No. 11/592,661,filed on Nov. 3, 2006, the disclosures of the aforesaid priorapplications are incorporated by reference herein in their entireties.

BACKGROUND

1. Field

The present invention relates to fasteners and, more specifically, to afastening system including a multi-piece, swage-type fastener and aswage tool therefore, which exhibit an optimum balance of low swage loadand high strength. The invention also relates to a simplifiedinstallation method using a low swage load fastening system.

2. Related Art

In many commercial applications, two-piece threaded or swaged fasteners,commonly referred to as lockbolts, are commonly used to secure a numberof workpieces together. See, e.g. U.S. Pat. Nos. 2,531,048; 3,215,024;3,915,053; 4,472,096; and 5,090,852. The material properties (e.g.,without limitation, tensile strength and hardness) of these fastenersvaries depending on the commercial application in which the fastenerswill be used. To distinguish the varying properties of fasteners, thefasteners are typically designated by Grade. The Grade of a fastener isindicative of its strength. Industry standards establish the requisitestrength of a fastener in order to meet a particular Grade, with thestrength of a particular fastener being determined by the strength ofthe material of the fastener bolt or pin. For example, a ½ inch Grade 5fastener has a ½ inch diameter pin or bolt shank portion for use in anominal ½ inch diameter workpiece opening and, in accordance with SAEJ429, Grade 5 or ASTM A-325, such Grade 5 fastener must have a minimumtensile strength of 120 KSI. By way of comparison, in order to qualifyas a Grade 8 fastener, per SAE J429, Grade 8 or ASTM A-490, the fastenermust have a minimum tensile strength of 150 KSI. Grade 5 fasteners areoften used, for example, in railroad (e.g., railcar) applications. Grade8 fasteners are commonly employed in commercial transportationapplications, for example, to secure truck components within thecommercial trucking industry.

Typically swage-type fasteners include a pin and a collar. Most of thesefasteners are of the pull-type variety and include a pin shank with alocking portion having lock grooves and a pull portion having pullgrooves. The pull grooves are adapted to be gripped by matching teeth inchuck jaws of an installation tool with a swage anvil. The swage anvilis adapted to engage the collar and apply a relative axial force betweenthe pin and collar, and to move over the collar and swage it into thelock grooves. The relative axial force comprises a combination of thetensile load on the pin caused by the chuck jaws and the compressiveload on the collar caused by the swage anvil. The pull portion of manyswage-type fasteners is connected to the lock groove portion by abreakneck groove of reduced strength. The breakneck groove is adapted tofracture at a preselected magnitude of axial or tensile force which isgreater than that required to swage the collar. Accordingly, the pullportion, or pintail, will be severed and removed from the pin shankafter completion of swaging. Other swage fasteners, however, have pullportions which remain on the pin after completion of installation. See.e.g., U.S. Pat. Nos. 5,315,755, 5,548,889 and 5,604,968 (disclosing athreaded pull portion which is not severed from the pin). In otherwords, these fasteners are pintail-less. See, e.g., FIGS. 1-8 of the'755 patent.

Among the problems frequently encountered with swage-type fasteners ofrelatively high strength (e.g., Grade 5 and above), is the excessivemagnitude of applied tensile load required in order to fully swage thecollar. This results in premature wear of the installation tool,particularly the pulling mechanism, and also stripping of the pullgrooves on the pin. The high swage load also complicates theinstallation process in general, especially where manually operatedinstallation tools are used. In an attempt to overcome some of thesedisadvantages, a variety of different installation tool modificationshave been made. For example, U.S. Pat. No. 4,299,519, which is herebyincorporated herein by reference as if fully set forth herein, disclosesan acorn-shaped pin pull portion and complimentary shaped tool grippingstructure which are intended to provide engagement of all of the pullgrooves of the pull portion by the gripping structure of the tool and,thereby resist stripping of the pull grooves. See, e.g., FIGS. 1-5 ofthe '519 patent. Other tools merely incorporate hydraulic and/orpneumatic piston-cylinders, in order to assist in applying the necessaryswaging force. See, e.g., U.S. Pat. Nos. 4,597,2613 and 4,878,372.However, this adds size and weight to the tool, which can make itawkward to handle or limit accessibility thereby potentiallyjeopardizing its precise application to drive the fastener and thus thequality of the final installation. Accordingly, there is room forimprovement of the installation tool and method for swage-type fasteningsystems.

The high swage load is largely the result of the use of fastener collarswhich have an increased wall thickness and are thus structured tooverfill or overpack the lock grooves in order to achieve the requisitestrength. for a particular fastener Grade (e.g., Grade 5 and Grade 8).See, e.g., U.S. Pat. No. 5,090,852, supra, (disclosing a modified pinthread form to include shallow grooves and a streamlined root contour,with the collar having an increased wall thickness with sufficientmaterial to overpack such shallow grooves, in order to achieve therequisite shear strength); see also the '755 patent, supra, and U.S.Pat. Nos. 5,548,889 and 5,604,968 (disclosing a shallow pin grooveconstruction and a collar shank with a volume having an excess ofmaterial of at least 16% in order to overpack the grooves). Overpackingof the lock grooves is problematic. It is a primary source of theaforementioned undesirable excessively high swage load. Accordingly,several attempts have been made, through variations in swage-typefastener design, to combat these disadvantages and, in particular, theprohibitively high swage load.

For example, U.S. Pat. Nos. 6,233,802 and 6,497,024, which are herebyincorporated herein by reference as if fully set forth herein, disclosea fastening system for a two-piece, swage-type fastener having a wide,shallow lock groove thread form which is designed to permit the fastenerto be installed at a lower swage load than a conventional swage-typefastener of comparable Grade yet retain essentially the same physicalproperties (e.g., tensile strength; clamp load) when installed. Thelower swage load permits the advantageous use of a smaller, lighterweight installation tool. The system is described as applied tofasteners having pintails as well as pintail-less fasteners. Forpull-type swage fasteners having threaded pull portions which are notsevered, as in the '755 patent, supra, the invention is stated tofacilitate the engagement of fewer threads on the pull portion becausethe extra force required to fracture a breakneck, is not required. Thisis said to (1) result in less stress on the engaged threads of themating threaded thimble or nut member of the pull tool, therebyextending tool life; (2) permit the use of a shorter, less expensive pinbecause less pin protrusion is required in order to grip the reducednumber of pull grooves which must be gripped; and (3) permit theinstallation tool to be smaller and thus lighter and less expensive,because lower applied loads are required for final installation. Thesystem also facilitates the use of an internal drive. See, e.g., FIGS.17 and 18 of the '755 patent (illustrating an internal drive including athreaded pull rod or spindle engageable within the pull grooves of athreaded bore in the end of the pin shank). As described in the '755patent and U.S. Pat. Nos. 5,548,889 and 5,604,968, which are herebyincorporated herein by reference as if fully set forth herein, use ofsuch internal drive allows for a reduction in protrusion relative to theexternal drive which, in turn, provides for a more efficient final fitand appearance of the fastener.

However, as disclosed in the '024 patent, supra, in order to achieve theforegoing benefits, it was necessary to change the thread form (e.g.,lock groove structure) to a wider and shallower configuration. Althoughrevising the thread form is a viable option to reduce swage load, thethread forth disclosed in the '024 patent is a drastic change requiringsignificantly larger pitch and a plurality of different radii with arelatively abrupt and discontinuous transition among the radii (e.g.from one radius to another). Producing pins with the disclosed threadform is, therefore, difficult and cost intensive. Additionally, thediscontinuous transition among radii of the thread form preventsmaximizing the complimentary engagement of the thread form by the collargrooves, when the fastener is swaged. There, therefore, is also room forfurther improvement in the thread form for pin lock grooves.

Additionally, collars of the type disclosed in the '802 and '024 patentshave a very narrow range of acceptable hardness, because too muchhardness results in a prohibitively high swage load and too littlehardness has insufficient strength. This is particularly problematicwith respect to higher Grade fasteners (e.g., Grade 5 and above) withwhich an increase in hardness of both the bolt and collar is required inorder to meet industry tensile strength requirements. Accordingly, knowncollars must be subjected to a thermal process in order to be softenough to swage and be compatible with the revised thread form, butstrong enough to meet industry Grade standards. This adds still furthercost and complexity to the manufacture of the fastener. For example, twosuch thermal processing methods include stress relieving and quench andtempering; obtaining consistent desired hardness by stress relieving isvery difficult to accomplish and quench and tempering is expensive anddifficult to accomplish without undesirably carburizing or decarburizingthe surface of the collars. Both methods are time and cost intensive,requiring, for example, the added expense of furnace operating costs.

It is, therefore, highly desirable to provide a high-strength, low swageload fastening system which exhibits, among other attributes, all of thebenefits of the low swage fasteners disclosed in the '519, '755, '802,and '024 patents, supra, but which, also does not require, for example,cost and time intensive thermal processing of the collar.

There is, therefore, room for improvement in the art of high-strength,low swage load fastening systems.

SUMMARY

It is an object of the present invention to provide a swage-typefastener that exhibits an optimum balance of reduced swage load and highstrength.

It is another object of the present invention to provide a fastener thatemploys an as-headed collar, which does not need to be thermallyprocessed (e.g., quench and tempered; stress relieved).

It is another object of the present invention to provide a high-strengthcollar with a reduced wall thickness, thereby reducing weight and theswage load, accordingly, while maintaining strength.

It is a further object of the present invention to provide an as-headedcollar having sufficient physical properties (e.g., hardness; strength),in order to meet a desired fastener Grade (e.g., Grade 5; Grade 8).

It is another object of the invention to provide a collar which may beemployed with existing fasteners and thread forms thereof, whileexhibiting the requisite strength of the desired Grade (e.g., withoutlimitation, Grade 5; Grade 8).

It is another object of the present invention to reduce the swage loadnecessary to set the fastener, thereby decreasing wear of installationtool components (e.g., without limitation, the swage anvil; thimbles;half shells) and increasing tool life.

It is yet another object of the present invention to provide a fastenerwhich eliminates expensive thermal processing steps (e.g., stressrelieving; quench and tempering) of the fastener collar.

It is still another object of the present invention to provide a collarwhich is employable with a wide variety of swage-type fastenersexpressly including, but not limited to fasteners with a pintail andpintail-less fasteners, such fasteners being new or part of an existinginventory with which the collar is retrofittable.

It is another object of the present invention to increase the collarhardness in order to maintain or improve the collar strength level, butdecrease the swage load by not overpacking the lock grooves of thefastener pin.

It is a further object of the invention to provide an improved fastenerlock groove thread form designed to overcome disadvantages experiencedby known shallow or waveform thread forms.

It is another object of the invention to provide a lock groove threadform which is structured to reduce swage load, while being relativelyeasy and thus economical to make.

It is yet another object of the invention to provide a complimentarypull groove and tool gripping structure configuration which provides,among other benefits, one or more of the advantages of improvingengagement between the pull grooves and gripping structure, extendingfatigue life of the gripping structure (e.g., thimble) by, for example,decreasing the diameter of the pin pulling section and increasing thethimble cross-section and thus the thickness and strength of the pullingthreads, and minimal protrusion length of the pull portion of the pin.

Therefore, it is a general object of the present invention to provide animproved, high-strength, swage type fastener and as-headed collartherefor, which can be installed at a reduced swage load with existingtooling and which exhibit optimum material properties (e.g., hardness;strength) of the desired fastener Grade, and to provide a low swage loadfastening system comprising one or more of, the as-headed collar, animproved pin pull portion and installation tool configuration, and asuperior fastener thread form.

These objects, and others, are met by the present invention whichprovides a low swage load fastening system and method.

In one embodiment of the invention, the fastener of the system mayinclude a collar having increased hardness and a reduced collar wallthickness adapted to avoid overpacking the lock grooves. The collar isvery economical to produce and easier to swage when compared with knownfasteners of comparable Grade. This is because the collar of the presentinvention is employed as-headed, thereby eliminating the costlyrequirement of a thermal treatment (e.g., quench and tempering; stressrelieving). The collar also does not require modification to the pinlock groove thread form. It is, therefore, readily employable withexisting pins and installation tools having a variety of different lockgroove thread loans, and its reduced swage load, which is attributableto its thin wall, extends installation tool life and/or allows lighterweight tooling. The fastener and collar therefor of the presentinvention, exhibit all of the foregoing advantages while furtherproviding the surprising and unexpected high-strength capabilitysufficient to meet Grade 5 and Grade 8 industry fastener standards.

Accordingly, the low swage load fastening system is for a swage-typefastener structured to secure a plurality of workpieces together. Theswage-type fastener includes a pin member having an elongated pin shankadapted to be located in aligned openings in the workpieces. The pinmember terminates at one end in an enlarged head adapted to engage asurface on one side of the workpieces and at its opposite end in agrooved portion adapted to extend past an opposite surface on theopposite side of the workpieces. The grooved portion of the pincomprises a locking portion having a plurality of lock grooves definedby circumferentially extending pin grooves and associated pin shouldersterminating in pin crests.

The fastener may be selected from the group consisting of pintailfasteners and pintail-less fasteners. The grooved portion of the pin ofthe fastener may be pintail-less and include an internal threaded borewherein the installation tool includes an internal drive structured tothreadingly engage the internal bore during swaging of the fastener.

In another embodiment of the invention, the low swage load fasteningsystem includes a pin having a substantially straight pull portionextending from the second end of the pin and including a plurality ofpull grooves. The pull portion has an outer diameter which is smallerthan the outer diameter of the locking portion of the pin. An associatedinstallation tool has a collet with a pull section for complimentarilyengaging the pull grooves of the pull portion. The protrusion length ofpull portion from the end of the pin is relatively short. Therefore, thepull portion may remain on the pin after swaging or may be removed byshaving it off or fracture of a breakneck groove that is optionallyprovided on the pin. The reduced diameter of the pull portion permitsthe installation tools to be thicker and stronger. The straight natureof the pull portion provides superior engagement by the installationtool.

The first tooth of the pull section of the installation tool may have agreater diameter than the remainder of the teeth of the tool, whichextends the tool life. The tool may be further improved, and the swageload further reduced, by including a relatively small swage load.

In yet another embodiment of the low swage load fastening system, thefastener pin may include a thread form defined by a number of blendedradii having a substantially smooth transition between each radius ofthe grooves of the thread form. Thereby improving engagement of thegrooves by the collar, when it is swaged. Such a thread form eliminatescomplexities in the thread rolling dies used to roll the threads.

In another aspect of the disclosure there is a low swage load fasteningsystem for a swage-type fastener structured to secure a plurality ofworkpieces together. The swage-type fastener includes a pin memberhaving an elongated pin shank adapted to be located in aligned openingsin the workpieces. The pin member terminates at one end in an enlargedhead adapted to engage a surface on one side of the workpieces and atits opposite end in a grooved portion adapted to extend past an oppositesurface on the opposite side of the workpieces.

The grooved portion comprises a locking portion having a plurality oflock grooves defined by circumferentially extending pin grooves andassociated pin shoulders terminating in pin crests.

An installation tool includes an anvil member with a swage cavity. Thereis an as-headed collar including a generally straight collar shankadapted to be swaged into said lock grooves on said pin member inresponse to a relative axial force or swage load applied between saidpin member and said as-headed collar by said installation tool.

A desired magnitude of clamp load on the workpieces which are fastenedtogether define a fastened joint. The swage cavity of said installationtool is structured to engage said collar shank and to swage it radiallyinward. The as-headed collar when swaged, has collar grooves andshoulders interlocking said pin grooves and shoulders. The pin memberand said as-headed collar is of different materials having ultimateshear stresses of different magnitudes in order that yielding of saidpin member is substantially avoided upon swaging said collar to said pinmember,

The collet has a protrusion from said collet thereby extending thelength of the pull section in a direction towards the collar thereby toincrease the contact area with said anvil.

The as-headed collar does not require thermal processing, and thegenerally straight collar shank of said as-headed collar has a wallthickness which is relatively thin thereby reducing the swage loadrequired to said as-headed collar.

The protrusion forms a flat circular face ahead of and adjacent to theleading thread of the collet, and then a circular forwardly angled faceahead of the flat face, and a second flat face, and an angular flat faceback tow a line of intersection with the outer diameter of the collet.

The end of the pull is not rolled down to a diameter position in linewith the base of the groove thereby to increase the shear strength ofthe end pull crest of the pull.

In yet a different aspect the last pull crest of the pull have a contourto conform with an enlarged puller radius of the last tooth of thecollet.

All of the foregoing low swage load mechanisms may be employedindividually or in any suitable combination. A swage-type fastener, anda method of securing a plurality of work pieces together using theaforementioned low swage load system, are also disclosed.

DRAWINGS

A full understanding of the invention can be gained from the followingdescription of the preferred embodiments when read in conjunction withthe accompanying drawings in which:

FIG. 1 is a cross-sectional view of the low swage load fastening systemand an as-headed collar therefor in accordance with an embodiment of theinvention, as employed on a swage-type fastener, having a pin thatincludes a removable pintail, with the fastener shown inserted throughaligned holes in two workpieces before being swaged by an installationtool, which is partially shown;

FIG. 2 is a cross-sectional view of the low swage load fastening systemand the as-headed collar of FIG. 1 as employed on a pintail-lessswage-type fastener, with the fastener shown after being swaged byinstallation tool, in order to secure two workpieces together;

FIG. 3 is a cross-sectional view of the low swage load fastening systemand the as-headed collar of FIG. 1 as employed on a pintail-lessswage-type fastener before being swaged by an installation tool havingan internal drive, in accordance with another embodiment of the presentinvention;

FIG. 4 is a plan view of a prior art collar for a swage-type fastener,with the inner bore of the collar shown in hidden line drawing;

FIG. 5 is an isometric view of the as-headed collar of FIGS. 1-3 whichhas a reduced wall thickness in accordance with an embodiment of thepresent invention, with a portion of the collar cut away for simplicityof illustration;

FIGS. 6A, 6B and 6C are cross-sectional specimen views of swagedfasteners having waveform, deep, and hybrid lock groove thread forms,respectively;

FIG. 7 is a cross-sectional view of an improved fastener pin pullportion and installation tool configuration in accordance with anembodiment of the invention and four sequential installation steps forswaging the fastener collar employing the improved pin pull portion;

FIG. 8 is a cross-sectional view of an end portion of the collet for theinstallation tool of FIG. 7;

FIG. 9 is a cross-sectional view of the anvil member of FIG. 7;

FIG. 10 is a cross-sectional view of an improved fastener pin pullportion and installation tool configuration in accordance with anembodiment of the invention and four sequential installation steps forswaging the fastener collar employing the improved pin pull portionusing a different collet; and

FIG. 11 is a cross-sectional view of an end portion of the differentcollet for the installation tool of FIG. 10.

DETAILED DESCRIPTION

Directional phrases used herein, such as upper, lower, front, back,etc., relate to the orientation of the elements shown in the drawingsand are not limiting upon the claims.

As used herein, the term “number” refers to one or more than one (e.g.,a plurality).

As employed herein, the term “as-headed” refers to a collar which isstrain hardened, for example, from cold working, rather than changinghardness using a thermal process (e.g., quench and tempering; stressrelieving). The collars of the present invention exhibit high strength(e.g., Grade 5 or 8 strength), without requiring thermal processing.

As used herein the phrase “low swage load,” is used for comparativepurposes to describe the reduction in required swage load afforded bythe features (e.g., as-headed collar; reduced diameter pintail pullportion; modified thread form) of the fastening system of the presentinvention in comparison with known fasteners of a similar Grade.Representative examples of such low or reduced swage load are quantifiedin the tables and corresponding disclosure herein.

Similarly, as used herein, the phrase “reduced wall thickness” is usedfor comparative purposes to describe the thinner wall structure of thecollar of the present invention in comparison with collars of knownfasteners of similar Grade. For example, the wall thickness of theexemplary collar is of reduced thickness, having less volume of materialand thus being structured not to overpack the lock grooves, unlike manyknown fasteners.

As employed herein, the term “pull portion” refers to the exemplary pinpull portion of the fastener pin and complimentary installation toolpull section for engaging the same. As will be discussed herein, theexemplary pull portion configuration comprises a substantially straight,reduced diameter, parallel side pull portion which protrudes lessdistance from the end of the lock groove portion of the pin than, forexample, the tapered, acorn-shaped pull portion and complimenting toolsection of U.S. Pat. No. 4,299,519, which is incorporated herein.

As employed herein, the phrase “thread form” refers to the exemplaryimproved pin lock groove thread form of the invention. The novel threadform is a hybrid in that, among other new features, the thread form is,in part, a hybrid of certain features of various thread forms. It will,however, be appreciated that various testing and experimentation wasrequired in order to develop the exemplary hybrid thread form andachieve the associated advantages attributable thereto.

While examples of fasteners of the present invention are defined withreference to certain specific sizes, i.e., nominal diameters, theconcepts can be readily extended to fasteners over a wide range of sizes(e.g., diameters; lengths).

As shown in FIGS. 1-3 and 7, the present invention relates tomulti-component (e.g., pin and collar) swage-type fasteners, such as,for example, the fasteners shown and described in the '024 patent,supra, which has been incorporated herein by reference. In FIGS. 1-3,6B, 6C and 7 comparable fastener components are numbered the same ineach of the Figures, but include the distinguishing designation of theletter “a” (FIG. 2), “b” (FIG. 3) “c” (FIG. 6B) and “d” (FIGS. 6C and 7)and, unless described otherwise, can be considered to be substantiallythe same. A first feature of the exemplary low swage load fasteningsystem 50, an as-headed collar 14 is shown as employed on each of thefasteners 10, 10 a, 10 b, 10 c and 10 d of FIGS. 1, 2 and 3, 6B, 6C and7 respectively.

FIG. 1 shows a fastener 10 including a pin member 12 with a pintail 41and the as-headed, low swage load collar 14 of the present invention.The pin member 12 has an elongated shank 15, which extends throughaligned openings or bores 16 and 17 in a pair of workpieces 18, 20,respectively, which are to be secured together. An enlarged, protrudinghead 22 at one end of the shank 15 engages the back surface 23 ofworkpiece 18. The shank 14 has a straight, smooth cylindrical shankportion 24 adjacent the head 22 which is adapted to be received withinthe aligned bores 16 and 17 with a clearance fit. However, it will beappreciated that in some installations the straight shank portion 24 canbe sized to provide a close tolerance or interference fit with one orboth of the bores 16 and 17. Adjacent and integral with the straightshank portion 24 is a locking shank portion 25 having a plurality ofcircumferentially extending, annular lock grooves 26.

The fastener 10 of FIG. 1, as previously discussed, includes a pintailor pull shank portion 41 having a straight annular land 42 followed by aplurality of annual pull groves 44. A breakneck groove 40 having areduced root diameter is located between the locking portion 25 and theannular land 42 of the pull portion 41 and defines the weakest sectionon the pin shank 15. The pull portion 41, including the land 42 and pullgrooves 44, is of a reduced diameter Da, relative to the diameter Db ofthe crests 71 of the locking grooves 26 of the locking portion 25.Diameter Db is also the same as that of the straight shank portion 24.It will be appreciated, however, that, in applications involving a closetolerance or slight interference fit (not shown) with the bores 16 and17, the crests 71 of the locking grooves 26 will be of a diametersmaller (not shown) than that of the straight shank portion 24. The pullgrooves 44 are adapted to be gripped by an installation tool 100 whichis employed to set the fastener 10 in the manner shown and described inthe '024 patent, supra.

Tooling 100 required for installation (e.g., swaging) of the collar 14can be generally constructed in a manner known to those skilled in theart and is, therefore, only partially shown for purposes of simplicity.In summary, the tool 100 has a nose assembly 102 with a plurality ofcircumferentially spaced jaws 104 adapted to grip the pull grooves 44 ofthe pull shank portion 41. Jaws 104 are located in a tubular colletassembly 106 which is slidably supported in an anvil housing 108, whichterminates at one end in a swage anvil section 110 having a swage cavity112. The jaws 104 are normally resiliently urged axially forward inconical tracks 114 to the radially closed position, shown, by a jawfollower assembly 116 (partially shown in FIG. 1). However, it will alsobe appreciated that, as discussed herein, that other suitableinstallation configurations (see, e.g., reduced diameter pintail pullportion 177 of FIGS. 7-9) and methods other than those shown anddescribed with respect to FIGS. 1-3 are contemplated by the exemplarylow swage load fastening system 50.

FIGS. 2 and 3 show the exemplary collar 14 as employed on tworepresentative varieties of pintail-less fasteners 10 a, 10 b,respectively. The Figures further illustrate how the exemplary collar 14is readily employable with a wide variety of known installation tools.For example, FIG. 2 shows an installation tool 200 including an externaldrive 202 with an internal threaded bore 204 and a sensing rod 206. Thisinstallation tool 200 is also discussed in detail in the '024 patent,which is incorporated herein. Briefly, the external drive 202 engagesgrooves 26 a and drives or applies a relative axial force on the swageanvil 210 such that it receives the collar 14 within the swage cavity212 and swages the collar 14 as the workpieces 18 a and 20 a are securedtogether.

FIG. 3 illustrates the exemplary collar 14 as employed with another typeof pintail-less fastener 10 b. The pin shank 15 b includes an internalthreaded bore 77 adapted for use with an installation tool 300 includingan internal drive 306 with a drive rod 302 having threads 304corresponding to the threads of the internal bore 77. Such installationtool is also shown and described in the '024 patent. In summary, theinternal drive 306 of the installation tool 300 engages the internalbore 77 of the pin shank 15 b and draws the swage anvil 310 toward thecollar 14 such that it is received and swaged within the swage cavity312.

Accordingly, it will be appreciated that the as-headed, low swage loadcollar 14 of the present invention may be employed with a wide varietyof fasteners, and tools therefor, including fasteners of both thepintail and pintail-less varieties, which have conventional annular orhelical lock groove thread forms with deeper and narrower grooves orreduced pitch in comparison with the modified thread form shown in FIGS.2-3 and described in connection with the invention of the '024 patent,supra. This is a significant improvement because, as will now be brieflydiscussed, although the structure of the fastener of the '024 patentresults in the requisite swage load being reduced to a manageablemagnitude, in order to do so, it requires a drastically changed threadform and the collar is heat treated (e.g., quench and tempered; stressrelieved) in order to achieve the necessary material properties (e.g.,strength). The collar 14 of the present invention, although applicablewith fasteners of the aforementioned revised thread form, (see, e.g.,FIGS. 2-3) may also be readily employed with fasteners having a moretraditional or conventional thread form with narrower and deeper lockgrooves. See e.g., FIGS. 7 and 7A and the accompanying disclosure in the'024 patent. As will be discussed herein, the exemplary as-headed collar14 may also be readily employed with the improved hybrid thread form 26d (FIG. 6) of the exemplary fastening system 50 of the invention.

Referring to FIGS. 4 and 5, a known prior art collar (e.g. 14′) iscompared to the exemplary collar 14 of the present invention. The collar14′ includes an enlarged optional diameter flange 59′ with a cylindricalshank 61′ and a through bore 65′. The collar shank 61′ is of a generallyuniform cylindrical configuration with a generally uniform wallthickness t′. The collar 14′ has a straight shank portion 69′ whichterminates at its outer end in a radially outwardly flared shank portion67′, also generally of thickness t′.

Like the exemplary collar 14 (FIGS. 1-3, 5 and 7) of the presentinvention, before being swaged, the collar 14′ is adapted to be disposedover the pin shank 15 (see, e.g., FIG. 1) and, with the workpieces 18,20 (FIG. 1) pulled together, will have the collar shank 61′ in radialalignment with the locking grooves 26 (FIG. 1). At the same time, theflange 59′ will be in engagement with the outer surface 73 of workpiece20. The workpieces 18 and 20 have a combined thickness t1 (FIG. 1)defining a nominal grip of the fastener (e.g., 10). However, it will beappreciated that the fastener 10 can be employed over a predeterminedgrip range, which varies from workpieces having a minimum totalthickness less than t1 (not shown) to a maximum total thickness greaterthan t1 (not shown).

As discussed in the '024 patent, which is incorporated herein byreference, the relative axial load required to swage the collar shank61′ is minimized by reducing the clearance between the straight collarbore portion 69′ of uniform diameter and the crests 71 (see, e.g.FIG. 1) of the lock grooves 26. In the invention of the '024 patent thisradial clearance is significantly reduced radially to around one half ofthat of the conventional lockbolt. See e.g., FIG. 7 of the '024 patent(illustrating the thread form of a typical swage-type fastener). Becauseof the close radial clearance provided by the minimized inside diameterID′, the outside diameter OD′ can be reduced to the thickness t′necessary to provide the desired volume. Thus, as discussed in the '024patent, the inside diameter ID′ and outer diameter OD′ are selected toprovide the desired wall thickness t′ of collar shank 61′ resulting inthe necessary volume of collar material for swage and the desired amountof lock groove fill, while providing the desired reduction in swageload.

However, as shown in FIGS. 4A, 7A, 8A and 9A of the '024 patent, anddiscussed in the accompanying disclosure, such fastener and collar 14′therefor, requires a modified thread form to include lock grooves 26,which are wider and generally shallower (comparing the modified groovestructures shown in FIGS. 4A, 8A and 9A of the '024 patent with theprior art fastener of FIG. 7A). Additionally, although the modifiedfastener thread form helps overcome the aforementioned high swage load,it also requires cost intensive thermal processing of the collar 14′ inorder to maintain the requisite material properties (e.g., strength).

Accordingly, in view of the foregoing known attempts to improveswage-type fastener design, it has been a well recognized, long standingdesire within the fastener art to provide an economical, high Gradefastener which exhibits an optimum balance of low swage load and highstrength. While the aforementioned fasteners have substantially met thegoal of reducing swage load, they have, thus far, only been able to doso through use of cost intensive collar heat treatment and modificationsto the thread form. Among the ways that the low swage fastening system50 of the present invention overcomes these disadvantages is byproviding the aforementioned improved collar 14 which is readilyemployable with a wide variety of existing fasteners and thread formsthereof, and, is employable as-headed, without requiring a heattreatment, while still exhibiting high Grade (e.g., Grade 5 and Grade 8)material properties (e.g., without limitation, strength). The collar 14is, therefore, retroactively employable with existing fasteners as animproved stand alone component, or alternatively in combination with theother low swage features of the exemplary fastening system 50.

FIG. 5 shows a more detailed, isometric view of the exemplary as-headed,low swage load collar 14, which is shown as employed with fasteners 10,10 a, 10 b, 10 c, 10 d in FIGS. 1-3 and 7, respectively. A portion ofthe collar 14 is cut away to illustrate the exemplary reduced wallthickness t of the collar 14 (compare, for example, to thickness t′ ofcollar 14′ in FIG. 4). Thus, for a fastener of comparable Grade, thecollar 14 of the present invention will have an inside diameter IDsubstantially equivalent to the outer diameter Db of the lock groovecrest 71 (FIG. 1), similar to ID′ of the collar 14′ of FIG. 4. However,the outside diameter OD of the exemplary collar 14 is less than OD′ ofthe prior art collar 14′, thereby resulting in the exemplary reducedwall thickness t of the collar shank 61. As will be discussed in greaterdetail herein, the reduced wall thickness t results in a smaller volumeof material to be swaged into the lock grooves (e.g., 26, 26 a, 26 b, 26c, 26 d of FIGS. 1-3, 6B, 6C and 7 respectively). This, in combinationwith the increased hardness of the exemplary collar 14, results in thelock grooves (e.g., 26, 26 a, 26 b, 26 c, 26 d) not being overpacked,which is directly opposite of many known prior art collar designs. Also,by reducing the collar ID, there is less distance traveled by the collarduring swage to engage the lock grooves. Less swage load is spent inswaging the collars of the present invention into the lock groovesbecause the collars have less clearance from the outer diameter of thecrests that the prior art. In prior art lockbolt systems, more clearancewas provided between the collars and the outer diameter of the crests sothat more swage load was applied to the collar to swage it through airbefore being swaged into the lock grooves. The reduced wall thickness t,not overpacking the lock grooves 26, 26 a, 26 b, 26 c and 26 d andreduced clearance between the collar and the outer diameter of thecrests of the lock bolt reduces the relative axial load required toswage the exemplary collar 14.

Accordingly, the present invention accomplishes the similar goal ofreduced swage load in a more economical, improved manner than the knownprior art. It will be appreciated that the exact difference or amount ofreduction in the wall thickness t of the exemplary collar 14 incomparison, for example, with wall thickness t′ of collar 14′, will bepartly dependent upon the size (e.g., without limitation, ½ inch, ⅝inch, ¾ inch) of the particular fastener at issue. For example, thedifference in collar wall thickness will likely be greater between apair of ¾ inch fasteners of comparable Grade, than, for example betweena pair of ¼ inch fasteners of comparable Grade. Examples of the effectsof the reduced thickness, t, of the collar shank 61 of the presentinvention, as well as representative numbers for such thickness, will befurther explained and appreciated through discussion of the followingexamples. The examples illustrate and discuss the results of severalexperiments conducted for the purpose of evaluating the effects ofreduced collar shank 61 wall thickness t on as-headed, high-strengthcollars 14 and fasteners (e.g., 10, 10 a, 10 b, 10 c and 10 d). Thefollowing examples are provided to further illustrate the improvementsand are not limiting upon the invention.

Example 1

The purpose of the first experiment was to determine if collars made toHS5CF-R12 dimensions could be used as-headed to meet Grade 8 values. TheHS5CF-R12 fastener is a commercially available Grade 5, swage-typefastener which is manufactured by Huck International, Inc. of Waco, Tex.

The experiment involved a test of the outer diameter (OD), hardness,swage load, tensile and preload of standard quench and tempered Grade 8collars which were tested and compared against as-headed Grade 5collars. The results are quantified in Table 1 herein below.

TABLE 1 Grade 5 As-Headed Collar Collar Description HS8CF-R12 Collar “A”Collar “B” Heat Treat Condition Quench- As- 900 F. Temper Headed StressCollar Hardness Rb77 Rb90 Rb89 Collar Outside Diameter .568″ .562″ .562″Tensile (Spec: 11,600 min.) 13,070 lbs.  12,400 lbs.  12,730 lbs. Percent over spec. 13%  7% 10% Preload (Spec: 7,400 min.) 8,390 lbs.8,040 lbs. 7,570 lbs. Percent over spec. 13%  9%  2% Swage Load 5,850lbs. 4,860 lbs. 4,800 lbs. Percent decrease from Standard 18% 18% HS7Minimum Swage 7,000 psi  5,700 psi  5,700 psi  Percent decrease fromstandard 19% 19%

As shown in Table 1, both Collars “A” and “B” had a swage load which was18% lower than the current standard HS8CF-R12 collar, and both meet theminimum industry tensile and preload requirements of Grade 5. Theexperiment uncovered that the as-headed collar, Collar “A”, had twodistinct advantages over Collar “B”:

1) Collar “A” does not require a heat treatment operation (e.g., quenchand temper; stress relieve), and therefore, also does not receive anadditional step of cleaning or decarburizing the collar; and

2) Collar “A” had a significantly higher preload margin above theminimum industry specification than Collar “B”.

Although Collar “A” did not have quite as high actual tensile andpreload as the current standard Grade 5 collar, it had a significantly(18%) lower swage load. Accordingly, the test confirmed that as-headedcollars having a reduced OD and thus wall thickness, in accordance withthe present invention, can economically achieve a reduced swage load(18%) while exhibiting optimum material properties.

Example 2

The second experiment arose out of the desire to develop an economicalway to improve installation tool life and to reduce the cost of makingGrade 8 collars. Specifically, the goal of the experiment was todetermine if thinner-walled, as-headed collars can increase snub load,decrease swage load, and maintain the same tensile and preload asstandard quench and tempered collars. Snub load is the load at which thecollar 14 first engages the pin lock grooves 26, 26 a, 26 b, 26 c, 26 d.After this point, sheet (e.g., workpiece 18, 20; 18 a, 20 a; 18 b, 20 b;18 c, 20 c) gap pull-out is restricted because the collar 14 is stuck onthe pin 12, 12 a, 12 b 12 c, 12 d. If a gap remains after snub, clampingis reduced because collar elongation goes into diminishing the gapinstead of stretching the pin 12, 12 a, 12 b, 12 c, 12 d.

HSCF-R20 collars from the same work order and raw material (50 KSItensile) were divided into four groups. HSCF-R20 collars arecommercially available collars which are manufactured by HuckInternational, Inc. of Waco, Tex.

Group 1 was the control group and was processed in the conventionalmanner (e.g., by quenching and tempering). Collar OD was 1.009″.

Group 2 was as-headed and had the collar OD turned down to 1.000″.

Group 3 was as-headed and had the collar OD turned down to 0.995″.

Group 4 was as-headed and had the collar OD turned down to 0.990″.

All of the collars were shot blasted and waxed to have the same surfacetexture and lubricant. Additionally, the same work order of pins wasused for all tests, as was the same installation tooling and the sametesting instruments. Three tests were made with each group for eachcategory of snub load, swage load, preload and tensile. To simplify thereport, only the averages of the tests are reported in Table 2 herein.

TABLE 2 Thin-Walled, As-Headed Collars Preload Lbs Tensile Lbs HardnessSnub Swage (26,080 (37,300 Rb Lbs Lbs min.) min.) Quench- Tempered 1009″OD  76 5,670 18,730 28,000 38,600 As-Headed 1.000″ OD  88 8,770 17,57028,670 41,570 .995″ OD 88 7,590 15,870 27,000 39,470 .990″ OD 88 7,30014,070 24,000 36,970

The collar OD tolerance range for standard collars is 1.006″ to 1.012″.Using the same tolerance range for as-headed collars, the allowablecollar OD range is between about 0.995″ to 1.001.″ As shown, the ODvalues in Table 2 range from about 0.990″ to 1.009″ and can be taken asthe minimum and maximum. The average values of 1.000″ and 0.995″ can,therefore, be compared directly against the 1.009″ nominal values.

As shown from the results quantified in Table 2, as-headed collars offerthe following advantages over standard quench and tempered collars:

1. Improved mechanical values: about 44% greater snub (gap pullout)load, about 11% lower swage load, about 5% more tensile strength and thesame preload. Preload is about 7% above the minimum industryspecification with both types of collars, but tensile strength improvesfrom about 3% over the minimum specification to about 9% overspecification when using the as-headed collar. The as-headed collar alsoprovides a decrease in installation tool pressure of about 10% to 20%which is a very significant advantage resulting in reduced tool wear,more accessible smaller tools and lighter weight tools.

2. Improved quality: Case and decarburizing problems are eliminated whencollars are not quenched and tempered. Additionally, consistency ofhardness remains the same because as-headed collars stay within ahardness range of about 10 Rb. It is also possible that certain quenchedand tempered collars might not meet tensile requirements if hardnessapproaches the minimum Grade specification of Rb 68. This is not aproblem with the increased hardness of the exemplary as-headed collars.

3. Reduced Cost: By eliminating heat treatment and the blast clean step,associated therewith, as-headed collars reduce manufacturing costs.Additionally, collar raw material costs can be reduced by replacingannealed AISI 1010 steel wire, which is commonly used to produce thecollars, with hot-rolled AISI 1006 wire, which may be used to producethe exemplary as-headed collars because it work hardens substantiallythe same amount as annealed AISI 1010 steel wire. As-headed collars maybe made from unannealed or annealed low carbon steel. It is alsounannealed and, therefore, less expensive.

4. Reduced lead time: Eliminating heat treatment and inspectionassociated therewith saves about two or three days of the time typicallyrequired to produce the collars.

Accordingly, the results of EXAMPLE 2 further confirm the advantages ofusing an as-headed collar in accordance with the present invention.Additionally, when viewed in conjunction with EXAMPLE 1, the ability ofthe fastener and collar therefor of the present invention to reduceinstallation tool component (e.g., anvil; thimble) wear and thusincrease tool life becomes evident. While anvil wear would be expectedto increase because the exemplary as-headed collars are harder, it hasbeen discovered through the present invention that, anvil wear will infact does not significantly change upon reducing the OD and thus wallthickness, t, of the exemplary collar 14 and thimble life is increasedas a result of the reduced tool pressure required.

Example 3

Further to the results of the first two experiments, the thirdexperiment further tested the effects of increasing collar hardnesswhile decreasing collar wall thickness, in an attempt to find an optimumbalance of high strength and low swage load. Gap pullout results in lessthan optimum clamp on the joint. However, increasing collar hardnessalso increases the swage force to install the collar, as evidenced inEXAMPLE 2. Decreasing the wall collar thickness lowers the swage forcedisproportionately more than the snub (gap pullout) load. Accordingly,combining the discoveries of the foregoing experiments, this experimentwas intended to overcome known fastener design limitations by balancingincreased collar hardness with a decrease in collar wall thickness inorder to maintain the same tensile and preload and increase snub loadwhile decreasing the swage load, thereby improving installation toollife. It was also a goal of the experiment to accomplish the foregoingwithout making a change to the standard pin or installation tool inorder to keep potential future changeover to the new collar as simpleand cost effective as possible.

For consistency, the same work order of collars was used throughout thetest. Collar wall thickness was decreased by machining down the collarOD in 0.010″ increments. Snub load, swage load, ejection load, preloadand tensile strength were inspected for the optimum wall thickness. Themost consistent way to significantly raise collar hardness, as learnedfrom EXAMPLES 1 and 2, was to leave the collars as-headed, which gave anet hardness increase of between about 20-25 Rb points. Once the optimumcollar wall thickness was determined, the same tests were done tocompare standard pins with pins of the type described hereinbefore inconnection with the 024 patent, the latter having been heat treated tothe same hardness and pinbreak. This was done to determine the effect oflock groove form. All testing was done on production test equipmentusing standard test procedures.

To simplify the report and because there was insignificant variationbetween tests, only the average value of three tests for each conditionis reported. Table 3 herein shows the result of the exemplary reducedcollar wall thickness when employed with pins of a standard thread form.

TABLE 3 Reduced Collar Wall Thickness Standard Thread Form Collar CollarCollar Snub Swage Eject Clamp Tensile Rb OD″ Wall″ Lbs Lbs Lbs Lbs LbsQuench Tempered 72 .990 .167 6,683 19,366 2,900 26,500 35,300 As-Headed92 .990 .167 11,366 20,766 2,950 29,250 39,666 As-Headed 92 .980 .16210,766 19,033 2,966 28,000 37,633 As-Headed 92 .970 .157 9,833 17,2772,839 26,250 33,366 As-Headed 92 .960 .152 8,633 13,433 2,048 18,75019,586

As can be calculated from Table 3, a calculated as-headed hard collar ODof 0.975″ would give identical clamp and tensile values as the currentstandard collar, but snub load would increase about 54%, and swage loadwould decrease about 6%. These results further confirm the attributes ofthe fastener and as-headed, thin-walled, low swage load collarstherefor, of the present invention.

Snub, clamp and tensile data for standard lock grooves (e.g., of thetype discussed with reverence to FIGS. 7 and 7A of the '024 patent) fromthis group validate the first group of data in Table 3. Swage load wasabout 1,300 lbs lower than predicted, or about a 12% reduction insteadof the original 6% reduction. There was no significant difference invalues due to lock groove thread form. There was a significant (about40%) reduction of swage load associated with a revised hybrid lockgroove in combination with the hard, thin wall as-headed collar withcomparison to the swage loads associated with a standard helical lockgroove thread form and a quench and tempered collar.

In summary, the experiment confirms that hardness can be increasedconsistently by using as-headed collars and collar wall thickness can bereduced because hoop strength is increased from such higher hardness.Reducing the OD of the collar to about 0.975″ creates no change inactual preload or tensile values, but increases gap pullout by about 50%and decreases swage by about 10%. Increased hardness of about 20 Rbpoints also increases calculated wear resistance of the collar by about40%, and no change is necessary in the pin or swage anvil in order toswage the as-headed collars. Accordingly, not only do the fasteners andcollars therefor of the fastening system 50 of the present inventionexhibit optimized physical properties, low swage load and economicefficiency, but the collars 14 may also be readily employed with a widevariety of existing fastener pins and thread forms thereof as well aswith the improved hybrid thread form 26 d (FIG. 6C.) of the invention.

It is desirable that the pin 12, 12 a, 12 b, 12 c, 12 d (FIGS. 1-3, 6B,6C and 7), be hard enough relative to the hardness of the collar 14 toresist crushing or excessive yielding in tension or necking down fromthe compressive swage loads. Therefore, in one form of the invention,for example, for the Grade 5 type fastener, the pin 12, 12 a, 12 b, 12c, 12 d could be made of AISI 1038 steel or AISI 1541 steel or othercomparable materials for the same Grade having a hardness of betweenabout Rc24 to about Rc35 and an ultimate tensile strength of at least120 KSI. Typically, conventional collars (e.g., 14′) for such fastenerswere made from AISI 1010 carbon steel, which had to be thermallyprocessed to between about Rb65 to Rb85 and an ultimate tensile strengthof at least about 60 KSI.

However, as previously discussed, the exemplary collar 14 is made, forexample, from AISI 1006 steel or any other suitable annealed orunannealed low carbon steel material. The AISI 1006 steel is notannealed. Unannealed steel wire, commonly referred to as “green” wire,is less expensive thereby making the exemplary collar 14 more economicalto produce. The pin 12, 12 a, 12 b, 12 c, 12 d has a sufficient hardnessto accept both the high tensile preloads desired and the swage loads onthe collar 14 without substantially yielding. In addition the collar 14,like the collars discussed, for example, in the '024 patent, can becoated with a conventional lubricant such as a water solublepolyethylene wax or cetyl alcohol. The collar 14 could also be zincplated. This assists in maintaining swage loads at the desired low leveland also minimizes wear of the swage cavity 112, 212, 312, 412. Thus, asshown through EXAMPLES 1-3, the shank 61 (FIG. 5) of collar 14 isprovided with a sufficient wall thickness t and, thus volume, in orderto insure that enough collar material will move axially in elongation,but at the same time it will have sufficient strength, such that the pinshoulders 60 (FIG. 1) and collar shoulders, formed during swage, remainin substantially full engagement as the design tensile load on the jointis reached. In this regard, the required wall thickness t (FIG. 5) ofthe exemplary collar shank 61 will increase slightly for larger diameterfasteners and decrease for smaller diameter fasteners, while remainingthin enough to exhibit the advantages discovered through the presentinvention, and thinner than known prior art collars of comparable sizeand Grade. Table 4 further summarizes the improvements of collar 14 byway of a comparison between known quench and tempered collars 14′ andthe as-headed collar 14 of the invention as employed with known Grade 5and Grade 8 fasteners 10, 10 a, 10 b, 10 c, 10 d and with the improvedGrade 5 and Grade 8 fasteners 10 c, 10 d (FIGS. 6 and 7) of theexemplary low swage load fastening system 50. The various collardimensions are shown for three different nominal fastener sizes ½ inch,⅝ inch, and ¼ inch. For the first-two types of fastener, the collardimensions of the existing quenched and tempered collar 14′ are shownfirst with the values of the as-headed collar 14 of the invention shownindented and offset to the right. Only the as-headed collar valves areshown for the Grade 5 and Grade 8 fasteners labeled “Next Generation”.These fasteners employ the exemplary hybrid thread form 126 (FIG. 6C) ofthe invention, which will be discussed herein.

TABLE 4 Dollar Dimension; Comparison ½″ Dia. ⅝″ Dia ¾″ Disc. CurrentC5OI. Grade Q/T'ed collar gap to bolt .021 .029 .034 Q/T'ed collar I.D..521 .654 .784 Q/T'ed collar O.D. .798 .987 1.184 Q/T'ed O.D./I.D. ratio1.532 1.509 1.510 Q/T'ed collar wall .139 .167 .200 As-headed collar gapto bolt .021 .029 .034 As-headed collar I.D. .521 .654 .784 As-headedcollar O.D. .789 .975 1.171 As-headed O.D./I.D. ratio 1.514 1.491 1.494As-headed collar wall .134 .161 .193 Current HP8/HF/HS Grade 8 Q/T'edcollar gap to bolt .022 .023 .033 Q/T'ed collar I.D. .521 .648 .783Q/T'ed collar O.D. .812 1.009 1.213 Q/T'ed O.D./I.D. ratio 1.559 1.5571.549 Q/T'ed collar wall .145 .180 .215 As-headed collar gap to bolt.022 .023 .033 As-headed collar I.D. .522 .648 .783 As-headed collarO.D. .803 .998 1.200 As-headed O.D./I.D. ratio 1.538 1.540 1.533As-headed collar wall .141 .175 .209 Next Generation Grade 5 As-headedcollar gap to bolt .010 .013 .016 As-headed collar I.D. .510 .638 .766As-headed collar O.D. .756 .945 1.134 As-headed O.D./I.D. ratio 1.4821.481 1.480 As-headed collar wall .123 .154 .184 Next Generation Grade 8As-headed collar gap to bolt .010 .013 .016 As-headed collar I.D. .510.638 .766 As-headed collar O.D. .766 .958 1.150 As-headed O.D./I.D.ratio 1.502 1.502 1.501 As-headed collar wall .128 .160 .192

As shown in Table 4, it has been found with the as-headed collar of thepresent invention that the ratio of the O.D. to the I.D. of an as-headedcollar is about: (i) 1.491 for an existing ⅝ inch Grade 5 fastener, (ii)1.540 for an existing ⅝ inch Grade 8 fastener, (iii) 1.481 for a 518inch next generation Grade 5 fastener, and (IV) 1.502 for a ⅝ inch nextgeneration Grade 8 fastener. A suitable range of the ratio of O.D. toI.D. for a collar of the present invention would likely be about 1.47 to1.55 or any other range falling within that range. Additional exemplaryembodiments of ranges are not set forth for the purpose of simplifyingthe specification. With the prior art quench and tempered collars, itwas found that the ratio of O.D. to I.D. of the collar is about: (i)1.509 for a ⅝ inch Grade 5 fastener and (ii) 1.557 for a ⅝ inch Grade 8fastener.

The reduction in swage load permits a reduction in the size of theinstallation tool (e.g., 100, 200, 300 of FIGS. 1-3, respectively; seealso installation tool 400 of FIGS. 7-9) resulting in a correspondingreduction in weight of up to 40% compared to the weight of conventionalinstallation tools. See, e.g., the '024 patent, supra, (discussing toolweight reduction as compared to the tool 148 of FIG. 7, therein).

In view of the fact that many fasteners (e.g., 10, 10 a, 10 b, 10 c, 10d) with which the collar 14 of the present invention may be employed,have pull portions and/or pintails of reduced size and/or length, it maybe desirable to provide a mechanism for holding the pin and collartogether when first pre-assembling it to workpieces, in preparation forinstallation. Therefore, the collar may optionally be provided with aflexible pre-assembly tab 90 (FIG. 5). See, e.g., U.S. Pat. No.4,813,834. The structure and operation of the optional assembly tab 90,if employed, would be much the same as disclosed in the '834 patent,supra, such disclosure being hereby incorporated herein by reference asif fully set forth herein. Briefly, the assembly tab 90 is located inthe countersunk bore portion 55 of collar 14 and is of a limitedcircumferential length. The assembly tab 90, as noted in the '834patent, supra, is preferably of a flexible construction and, as such,can be made of a plastic material such as, for example, polyurethane.The tab 90 extends radially inwardly a distance sufficient to be locatedwithin the lock grooves such as grooves 26, 26 a, 26 b, 26 c, 26 d. Inthis manner, once located in one of the lock grooves, the collar 14 willbe held onto the associated pin 12, 12 a, 12 b, 12 c, 12 d. The tab 90is located within the countersunk bore portion 55 which is at a point inline with the flange 59. Optional tab 90 facilitates movement of thecollar 14 onto the pin and the indexing of the tab 90 over the lockgroove crests. It will be appreciated that the tab 90 couldalternatively be located at the opposite end of the collar 14. It willalso be appreciated that the collar need not employ the optional tab 90.

It will also be appreciated that one or more portions of the collar 14may be of a different configuration than that which is shown anddescribed in herein. For example, the collar could be flangeless (notshown) or may have a flange of reduced size (not shown) and/or thecollar might not include the countersink bore portion 55. Additionally,the collar 14 may optionally include such a countersink bore portion atthe opposite end of the collar (not shown). It will also be appreciatedthat, as discussed in U.S. Pat. No. 4,867,625, the optional assembly tab(e.g., 90) may comprise a more substantial, limited thread (not shown)of a preselected extent such that some magnitude of initial clamp of theworkpieces can be attained in addition to holding the collar 14 andassociated pin in a pre-assembled condition with the workpieces. Seee.g., the '625 patent (incorporated herein by reference the disclosurerelating to the limited female thread as if fully set forth herein).

Another means by which the low swage load fastening system 50 of theinvention reduces swaging loads is shown in FIG. 6C and in particular,by way of comparison of FIG. 6C with FIGS. 6A and 663. Specifically, asshown in FIG. 6C, a hybrid thread form 26 d is provided for the lockgrooves 26 d of the pin 12 d which improves upon known thread forms suchas the waveform lock groove 26 b and deep lock groove 26 c examples ofFIGS. 6A and 6B, respectively. The exemplary thread form of FIG. 6C isdefined by a unique hybrid of features including a number of blendedradii which provide a substantially smooth transition between the crests28 d, 30 d and base of the lock grooves 26 d. More specifically, thefirst crest 28 d has a first radius R1, the second crest 30 d has afourth radius R4, and two intermediate radii R2, R3 define the baseportion or valley 132 of the groove 26 d while simultaneously smoothlyinterconnecting first radius R1 and fourth radius R4. In this manner thehybrid thread form 26 d (FIG. 6C) improves upon the relatively unsmoothand abrupt transition of the shallow and deep thread forms 26 b, 26 c ofFIGS. 6A and 6B, respectively. In particular, the relatively shallowwaveform 26 b of FIG. 6A requires many more radii and has a relativelydiscontinuous transition between and among the radii, and the deep lockgroove thread form 26 c of FIG. 6B has a relatively sharp, unblendedtransition between radii. Additionally, the waveform 26 b of FIG. 6A hasa wide pitch 36 b and relatively shallow depth 38 b, while the deepthread form 26 c of FIG. 6B conversely has a relatively narrow pitch 36c and a much larger depth 38 c, as shown.

As can be appreciated with continued reverence to FIGS. 6A and 6B,respectively, the relatively shallow waveform 26 b tends to overpackwhen the collar 14 is swaged, which as previously discussed,disadvantageously increases swage load. Conversely, as shown. the abruptchanges in the deep thread form 26 c of FIG. 6B tend to have theopposite effect, with less than the desired amount of engagementoccurring between the lock grooves 26 c of the pin 12 c and the collar14, when it is swaged.

Referring now to FIG. 6C and comparing the exemplary hybrid thread form26 d with thread forms 26 b and 26 c of FIGS. 6A and 6B, respectively,it will be appreciated that the hybrid thread form has a somewhatintermediate pitch 36 d and depth 38 d. This, in combination with theaforementioned blended radii R1, R2, R3, R4 provide a smooth, blendedthread form 26 d which accordingly promotes the complimentaryinterlocking engagement of the collar grooves 62 with the lock grooves26 d when the collar 14 is swaged, thereby reducing swage load. Theadvantages of the exemplary thread form 126 can be further appreciatedby the following table of values, Table 5, which summarizes anon-limiting comparative example of values for three different Grade 8,⅝ inch fasteners having pins 12 b, 12 c, 12 d with the different threadforms 26 b, 26 c, 26 d shown and described with respect to FIGS. 6A, 6Band 6C.

TABLE 5 Thread Fore Comparison ⅝ inch Grade 8 Fastener Type of ThreadLock Groove Pitch Swage Load Form Depth (inches) (inches) (lbs.) Waveform Lock 0.027 0.130 16,600 Groove Deep Lock Groove 0.032 0.091 14,400Hybrid Lock Groove 0.028 0.100 14,700

The deep lock groove thread form set forth in Table 5 was developed toreduce the problems associated with stripping the internal threaded bore204 depicted in FIG. 2. It was found that increasing the depth of thelock grooves 26 c was helpful in reducing damage to the internalthreaded bore 204. Thereafter, it was determined that deep lock grooves26 c were not necessary with a pull type mechanism 177 of the type shownin FIG. 7. The hybrid lock groove thread form set forth in Table 5 wasdeveloped for use with the pull mechanism 177 of the type shown in FIG.7.

As shown, the hybrid lock groove thread form 26 d (FIG. 6C) has arelatively intermediate depth 38 d and pitch 36 d when compared with thewaveform and deep lock groove thread forms 26 b, 26 c, respectively,while achieving all of the foregoing advantages, including maintaining areduced swage load generally comparable to the deep lock groove 26 c ofFIG. 6B. It will also be appreciated that the exemplary hybrid threadform 26 d could be employed in combination with the aforementionedas-headed collar 14, in order to even further reduce swage loads. By wayof example, for the ⅝ inch Grade 8 fastener of FIG. 6C and table 5, areduction in swage load of about 11% from the wave form lock groove canbe expected when the exemplary hybrid thread form 26 d of FIG. 6C isused in combination with the aforementioned as-headed collar 14. Also,for the ⅝ inch Grade 8 fastener of FIG. 6C and Table 5, a reduction inswage load of about 40% from a standard helical lock groove thread formcan be expected when the exemplary hybrid thread form 26 d of FIG. 6C isused in combination with the aforementioned as-headed collar 14.

It has been found with the as-headed collar of the present inventionthat the ratio of the shear strength between a pin and a collar isabout: (i) 1.8 for a Grade 8 fastener and (ii) 1.6 for a Grade 5fastener. A suitable range of the ratio of shear strengths between a pinand a collar of the present invention would likely be about 1.5 to 2.1or any other range falling within that range. Additional exemplaryembodiments of ranges are not set forth for the purpose of simplifyingthe specification. With the prior art quench and tempered collars, itwas found that the ratio of shear strength between a pin and a collar isabout: (i) 2.5 for a Grade 8 fastener and (ii) 2.2 for a Grade 5fastener.

It has also been found with the as-headed collar of the presentinvention that the lock grooves are typically packed: (i) about 40% forthe deep lock groove 26 c thread form and about 60% for the hybrid lockgroove 26 d thread form for a Grade 8 fastener and (ii) about 30% forthe deep lock groove 26 c thread form and about 50% for the hybrid lockgroove 26 d thread form for a Grade 5 fastener. Use of the deeper lockgroove with less than an overpacking of the lock grooves has been founddesirable from the standpoint of accommodating painted finishes that areapplied to the pin which accumulate in the troughs of the lock grooves.

It has also been found that the typical ratio of the pitch length to thedepth of the lock groove is about 2.8 for the deep lock groove threadform and about 3.6 for the hybrid lock groove thread form. A suitablerange of the typical ratio of the pitch length to the depth of the lockgroove would likely be about 2.5 to 4.0 or any other range fallingwithin that range. The prior art wave form lock groove had a typicalratio of the pitch length to the depth of the lock grooves of about 4.8.

FIGS. 7, 8 and 9 show still further mechanisms for lowering swage loadsand. thus increasing installation tool life, in accordance with theinvention. Like the hybrid thread form 26 d and as-headed collar 14previously discussed, the following low swage load mechanisms can alsobe employed independently or in any suitable combination with one orboth of the aforementioned hybrid thread form 26 d (FIG. 6C) andas-headed collar 14 (FIGS. 1-3, 5, 6A, 6B and 6C).

FIG. 7 shows a fastener 10 d and installation tool 400 for securing twoworkpieces 18 d, 20 d together wherein the fastener has a pull mechanism177 comprising a substantially straight, relatively short pull portion179 at the second end 19 of the pin 12 d. Additionally, four sequentialsteps are shown for installing the fastener 10 d using the exemplary lowswage load system 50 in accordance with a method of the invention.

The pull section 179 of the pin 12 d has a relatively short length 183and thus extends or protrudes from the second end 19 of the pin 12 d ashort distance. In fact, the protrusion length 183 of the exemplary pullsection is so short that, unlike the acorn-shaped pull section of U.S.Pat. No. 4,299,519 (see, e.g., FIGS. 1-5) which has been incorporated byreference herein, the pull section 179 of the invention is not intendedto be severed following installation, although severance of the pullsection 179 is conceivable by using a breakneck groove on the pin 12 dor shaving off the pull section 179 with a sharing tool in otherembodiments of the invention (not shown). This advantageously eliminatesshock loading of the installation tooling 400 known to be caused by thesudden fracture of a break neck groove (see, e.g., break neck groove 40of. FIG. 1). It also eliminates pintail debris, and pinbreak noise. Thepreferred embodiment of the acorn-shaped pull portion of the '519 patentsuffers from these disadvantages. More specifically, by way of example,for a ⅝ inch Grade 8 fastener 10 d, the exemplary pull section 179protrudes about 0.10 inches or less than the acorn-shaped pull sectionof the '519 patent. Also unlike the acorn-shaped pull section of the'519 patent, the exemplary pull section 179 extends substantiallystraight with all of the pull grooves 181 having substantially the samediameter D_(B), which is smaller than the outer diameter D_(a) of thelocking portion 25 d of the pin 12 d, as shown. As will be discussed,the straight, reduced diameter D_(B) configuration of the exemplary pullportion 179 promotes better engagement by the installation tool 400 andextended tool life. It is also significantly easier to manufacture than,for example, the tapered acorn-shaped configuration of the '519 patent,wherein each groove of the pull portion of the pull portion has adifferent diameter.

Other improvements of the fastening system 50 of the invention are alsoshown in FIGS. 7, 8 and 9. Specifically, the exemplary installation tool400 for installing fastener 10 d includes a collet 402 having a pullsection 404 with a plurality of teeth 408 structured to complimentarilyengage the grooves 181 of the pull portion 179 of the pin (e.g., pin 12d), and an anvil member 410 having a swage cavity 412 for swaging thecollar 14, as previously discussed. The reduced diameter D_(B) butgenerally straight configuration of the exemplary pull portion 179allows the cross-sectional thickness T (FIGS. 7 and 8) of the collet 402(FIGS. 7 and 8) to be increased. Specifically, the thickness T can beincreased up to the full amount of the difference in diameters D_(a)′and D_(B) of the pin lock portion 25 c and pull portion 179,respectively. This makes the installation tool 400 stronger, thus givingit a longer fatigue life. The exemplary reduced diameter pull portion179 also results in less material being required for the manufacture ofthe pull portion 179 as compared, for example, with pull and lockingportion 25 a of fastener 10 a of FIG. 2. This in turn allows for thepull grooves 181 of the exemplary pin pull section 179, and thecorresponding teeth 408 of the installation tool pull section 404 tohave a greater thickness, thereby reducing stripping and galling of thepull grooves 181. Stripping and galling of the pull threads are alongstanding known disadvantage in the art. The first few threads of thetapered acorn design of the '519 patent may be susceptible to strippingand galling as wherein those threads have a reduced diameter, and. thusreduced strength and resistance to stripping.

As noted, FIG. 7 also shows the general method of installation using theexemplary low swage load fastening system 50 of the invention.Specifically, as shown, in operation, once the pin 12 d is insertedthrough aligned openings 16 d, 17 d in workpieces 18 d, 20 d, the collar14 is applied over the second end 19 of the pin 12 d. As previouslydiscussed the collar may, but need not necessarily be the aforementionedexemplary as-headed collar 14. The pull portion 179 of the pin 12 d isthen engaged by collet 402 of the installation tool 400. The exemplarycollet is a split gripper collet 402 which expands to an open position(FIG. 7, top illustration) and contracts to a constricted or closedposition (FIG. 7, second illustration from the top) wherein the teeth408 of the collet pull section 404 complimentarily substantially fullyengage the pull grooves 181 of the pull portion 179. The installationtool 400 is then actuated thereby drawing the collet 402 into the swageanvil 410, and closing the pull section 404 of the collet 402, in orderthat the collet 402 pulls the pin 12 d and collar 14 into the swagecavity 412 of the anvil 410 thereby applying a radially inward swageload. and swaging the collar 14 into the pin lock grooves 26 d. Thesensing rod 406 then detects when the swaging operation is complete bysensing when the pin 12 d has been completely pulled, and accordinglydeactivates the installation tool 400 withdrawing the collet 402,releasing the pull section 179, and ejecting the collar 14 from theanvil 410. Accordingly, the exemplary installation system 50 and methodgreatly improve and simplify fastener installation by achieving all ofthe advantages of a pintail-less installation while avoiding associateddisadvantages like the required higher wear spin on thimble, which isreplaced by the long wear collet 402. This also eliminates a pluralityof other separate installation tool components such as a separatecollet, release ejector, separate jaws, and follower and spring. andreplaces them with essentially one part, the exemplary split grippercollet 402. In this manner the invention reduces the installation cycletime, cost, and complexity of know spin on engagements and providestooling which is faster, lighter, quieter, and which contains lessmoving parts, equating to a significant cost savings.

It will be appreciated that other installation methods andconfigurations other than those shown and described herein, could beemployed. For example, as previously discussed, it is conceivable that aseverable pin pull section (not shown) or an inner drive pull mechanismconfiguration (not shown) could be employed without departing from thescope of the invention. It will also be appreciated that while the pullsection 179 is shown as having annual pull grooves 181, other threadforms (e.g., without limitation, helical threads) could conceivably beemployed if corresponding modifications were also made to theinstallation tool.

The improvements of the exemplary installation tool 400 afforded by theexemplary pin pull portion configuration are further appreciated withreference to FIGS. 8 and 9.

FIG. 8 shows part of the pull section 404 of the exemplary split grippercollet 402 for installation tool 400. The pull section 404 has anengagement end 405 (oriented to the left in FIG. 8) and a plurality ofteeth 408. In the example of FIG. 8, the pull section 404 has four teeth408. The first tooth 409, which is adjacent the engagement end 405 has afirst inner diameter ID₁. The remainder of the teeth 408 have a secondinner diameter ID₂, which is less than By opening up the inner diameter,ID₁, of the first pulling tooth 409, as shown, the collet design of theinvention resists chipping of that tooth 409.

Specifically, the vertex (shown in phantom line drawing in FIG. 8) ofthe exemplary first tooth 409 is removed to open up the inner diameter,ID₁, at that location. This in turn moves the primary point of loadingfrom this location to one that is further back within the pull section404, (e.g., to the right with respect to FIG. 8), thereby reducing themoment loading on the furthest forward root radius r of tooth 409 andthus increasing fatigue life of the collet 402. More specifically, byway of example with reference to the first tooth height h in the exampleof FIG. 8, a reduction in tooth height of about 30% results in adramatic increase in tool 400 fatigue life to about 24,000 installationcycles at about 12,000 pounds swage pressure for a Grade 5 fastener,having the exemplary pull section 179 (FIG. 7), whereas the front tooth409 previously failed at 14,000 cycles. This dramatic improvementresulted, as previously discussed, from reducing the movement arm on thefront tooth 409 by increasing the 1D₁, which shifted the failure modeback to a more robust area (e.g., the fourth tooth 408 from the left) ofthe pull section 404 of the collet 402. This improvement is in additionto the aforementioned increase in tool life afforded by the greater wallthickness T of the collet 402. Additionally, as previously discussed,all of this is achieved through use of the exemplary single componentsplit gripper collet 402, which is adapted to expand and constrictwithout requiring separate jaws, a separate ejector, or a separatefollower and spring. This is because the exemplary split gripper collet402 includes one or more slits (not shown) which make it constrictablefrom a relaxed or open position (top illustration of FIG. 7) to a closedor constricted position (second illustration of FIG. 7) by being drawninto the inner bore 420 (Figure e)) of the anvil 410 which exerts aradially inward force in order to close the collet pull section 404. Itwill, however, be appreciated that any known or suitable alternativecollet design (not shown) having, for example, without limitationseparate closeable jaws (not shown) could be employed to, for example,engage and pull the pin pull portion 179 (FIG. 7).

FIG. 9 shows yet another advancement of the exemplary low swage loadfastening system 50.

Specifically, the exemplary swage anvil 410 includes the swage cavity412, which. as shown, has a radiused entrance section 414 in order tofacilitate initial engagement with the collar 14 (FIG. 7), a swage land416, and an inner bore 420. The swage land 416 has a first diameter D₁,and the inner bore 420 has a second diameter D₂, which is greater thanthe first diameter D₁. Accordingly, the inner bore diameter D₂, whichopens up behind the swage land 416, relieves compressive swage load onthe collar 14 (FIG. 7). This is made possible by the relatively narrow(i.e., small) nature of the exemplary swage land 416 (best shown in thesectional close-up view of FIG. 9). The narrow width 418 of the swageland defines a small swaging area because it then opens into the largerdiameter D₂ inner bore 120, as opposed to having a continuous singlediameter for substantially the entire length L. of the swage anvil 410.The increased diameter, D₂, of the inner bore 420 of the exemplary anvil410 also provides space to accommodate the thicker and thus strongerwall thickness T of the collet 402 (FIGS. 7 and 8), thereby furtherincreasing tool life. Furthermore, the length L, of the improved anvil410 of the invention, may also be shortened, as compared, for example,to anvil 110 of FIG. 1. Accordingly, the low swage load fastening system50 of the invention also provides a number of installation tool 400improvements by reducing the number parts for the tool, decreasing theweight of the tool, reducing swage loads required by the tool, reducingthe cost to make the tool, and increasing the expected life time of thetool.

With reference particularly to FIGS. 6A, 6B and 6C, the details of theinteraction of the collar and bolt are shown. When the collar firsttries to the pull the bolt in preload, the collar is not strong enough,so the first bolt crest shears the collar, creating a void and rollingup collar material in front of the bolt crest. The same thing happens toa lesser extent on the second bolt crest. Finally, there is enoughcollar material engaged onto the bolt so voids and roll-up do not occur.This happens sooner with as-headed collars that are harder thanquench/tempered collars because they have higher shear strength. Hardercollars stretch the bolt sooner and create more preload.

FIG. 10 is a cross-sectional view of an improved fastener pin pullportion and installation tool configuration in accordance with anembodiment of the invention and four sequential installation steps forswaging the fastener collar employing the improved pin pull portionusing a different collet. The system there shown is similar to FIG. 7.In FIG. 11, which is similar to FIG. 8 there is a cross-sectional viewof an end portion of the different collet for the installation tool ofFIG. 10.

In the disclosure of FIGS. 10 and 11 there is a low swage load fasteningsystem for a swage-type fastener structured to secure a plurality ofworkpieces together. The swage-type fastener includes a pin memberhaving an elongated pin shank adapted to be located in aligned openingsin the workpieces. The pin member terminates at one end in an enlargedhead adapted to engage a surface on one side of the workpieces and atits opposite end in a grooved portion adapted to extend past an oppositesurface on the opposite side of the workpieces.

The grooved portion comprises a locking portion having a plurality oflock grooves defined by circumferentially extending pin grooves andassociated pin shoulders terminating in pin crests.

An installation tool includes an anvil member 410 with a swage cavity.There is an as-headed collar 14 including a generally straight collarshank adapted to be swaged into said lock grooves on the pin member inresponse to a relative axial force or swage load applied between the pinmember and the as-headed collar by the installation tool.

A desired magnitude of clamp load on the workpieces which are fastenedtogether define a fastened joint. The swage cavity of said installationtool is structured to engage said collar shank and to swage it radiallyinward. The as-headed collar when swaged, has collar grooves andshoulders interlocking said pin grooves and shoulders. The pin memberand said as-headed collar is of different materials having ultimateshear stresses of different magnitudes in order that yielding of saidpin member is substantially avoided upon swaging said collar to said pinmember.

The collet 600 has a protrusion 602 from said collet thereby extendingthe length 604 of the pull section in a direction towards the collar 14thereby to increase the contact area with the anvil 410. Extendingpuller length increases contact area with anvil which decreases pressureand galling. It also allows for lead angle as puller returns throughsmaller anvil bore.

The as-headed collar does not require thermal processing, and thegenerally straight collar shank of the as-headed collar has a wallthickness which is relatively thin thereby reducing the swage loadrequired to the as-headed collar.

The protrusion 600 forms a flat circular face 600 ahead of and adjacentto the leading thread 608 of the collet 600. Then there is a circularforwardly angled face 610 ahead of the flat face 606. There is a secondflat face 612, and an angular flat face 614 back to a line ofintersection 616 with the outer diameter of the collet 600. The shearstrength of the last bolt crest is increased by not rolling down theheaded blank diameter at the end of the bolt.

The end 618 of the pull 620 is not rolled down to a diameter position inline with the base 622 of the groove 624. This increases the shearstrength of the end pull crest 626 of the pull 620. The puller teethshears bolt threads off at line 636.

The last pull crest 626 of the pull has a contour 628 to conform with anenlarged puller radius 630 of the last tooth 620 of the collet 600.

Also, the shortened first puller tooth 632 increasing its thickness 634thus reduces chipping.

In view of the foregoing, the invention provides a low swage loadfastening system and method with numerous improved fastener andinstallation tool features, including an as-headed collar, a hybrid lockgroove thread farm, an improved pin pull section, and a variety ofinstallation tool improvements, all of which independently, and in anysuitable combination, lower swage loads and improve the installation ofswage-type fasteners.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of invention which is to be given the fullbreadth of the claims appended and any and all equivalents thereof.

What is claimed is:
 1. A collet for a fastener installation tool,comprising: a pull section with a fastener engagement end and aplurality of teeth, wherein the plurality of teeth includes a firsttooth located proximate to the fastener engagement end, wherein thefirst tooth of the plurality of teeth includes a first inner diameterand each of the remainder of the plurality of teeth includes a secondinner diameter, wherein the first inner diameter of the first tooth isgreater than the second inner diameter of each of the remainder of theplurality of teeth.
 2. The collet of claim 1, wherein the plurality ofteeth includes four teeth.
 3. The collet of claim 1, wherein the pullsection includes a cross-sectional thickness, wherein the collet isadapted to engage a pin member having a locking portion and a pullportion extending from the locking portion, the locking portion of thepin member having a first outer diameter and the pull portion of the pinmember having a second outer diameter that is smaller than the firstouter diameter of the locking portion of the pin member, wherein anincrease in the difference between the first outer diameter of thelocking portion of the pin member and the second outer diameter of thepull portion of the pin member allows for a corresponding increase inthe cross-sectional thickness of the collet, thereby extending thefatigue life of the installation tool.
 4. The collet of claim 1, whereinthe collet is a single split gripper collet, wherein the pull section ofthe split gripper collet is movable between an open expanded positionand a closed constricted position.
 5. The collet of claim 1, wherein thepull section includes a protrusion extending from the fastenerengagement end, thereby extending the length of the pull section of thecollet.
 6. The collet of claim 5, wherein the protrusion includes afirst face located ahead of and adjacent to the first tooth of theplurality of teeth, a second face extending angularly beyond and awayfrom the first face, a third face located adjacent to the second face,and a fourth face extending angularly back towards the first face. 7.The collet of claim 6, wherein the first and third faces of theprotrusion are parallel to one another.